The present application relates to an apparatus for measuring a turning rate and, more particularly, to an apparatus for measuring the turning rate of a motor vehicle.
An apparatus of this type is known comprising a sensor system which generates a signal according to a turning rate based on a certain measurement principle and a signal processing means which determines the turning rate from a signal supplied to it.
The use of a turning rate sensor, which operates for example according to the principle of the vibrating gyrometer, is already known in connection with systems for controlling vehicle dynamics of motor vehicles. These sensors are based on detection and analysis of the Coriolis acceleration.
This type of turning rate sensor is known, for example, from U.S. Pat. No. 4,759,220. The sensor comprises a thin-walled hollow cylinder made of elastic material, in which a plurality of piezoelectric sensor elements are arranged. At least two of these sensor elements are arranged over each other in this sensor. These sensor elements are set into a constant mechanically driven oscillation with the help of an oscillator loop or guide. The Coriolis effect together with a turning speed coupled perpendicularly to the driven oscillation causes a Coriolis acceleration, which causes a deflection of the driven oscillator in the Coriolis direction. This deflection is a measure of the coupled turning rate. The resulting output voltage is analyzed with the help of a detector circuit and finally for determination of the turning rate.
Other oscillating structures are used for determining turning rate besides rotationally symmetric structures. These are, for example, oscillating rods or oscillating forks. Also micromechanical systems can be used which utilize the Coriolis force in oscillating systems in many ways. All these oscillating systems have disadvantageous null point stability problems and the sensitivity drift because of temperature variation and over lifetime. Satisfactory characteristic values can be obtained only with high manufacturing expense and testing efforts in which the problems of detection of offset and of sensitivity errors cannot be entirely avoided.
It is also possible to use the so-called Sagnac Effect in fiber optic gyroscopes for measurement of turning rate. At best they are in a position to fulfill the technical requirements for use in a motor vehicle, but at the current time they cannot be manufactured economically.
An additional possibility for measurement of the turning rate comprises use of an external observer, in the simplest case the earth's magnetic field, whose direction is measured with magnetic field sensitive sensors and/or with an electronic compass. The time dependent change of angle between the earth's magnetic field and the turning vehicle is measured in a suitable electronic circuit as the momentary turning rate. Disadvantageous problems can arise with this method however because of short duration disturbances of the earth's magnetic field, which for example are produced by steel bridges, by passing vehicle or rails. This type of disturbance can certainly make reliable evaluation of a rotation angle and/or a turning rate difficult.